let fs = require('fs')
let path = require('path')
let rs = fs.createReadStream(path.join(__dirname, 'req.txt'), {highWaterMark:3})
// 监听readable 就是暂停模式
rs.on('readable', function(){
    // 把缓存区读空 
    let data = rs.read()
    console.log(data)
})